MySQL 拒绝带有 ON DELETE SET NULL 但不是 ON DELETE CASCADE 的列

Question

我有一个简单的 MySQL 数据库，在某些 table 列上有一些外键。一些外键列被设置为 ON DELETE SET NULL，它似乎工作正常。但是，对于其中一个 table，我无法配置 ON DELETE SET NULL - 我只能配置 ON DELETE CASCADE。

最初的 table 看起来像这样：

CREATE TABLE sessions(
session_id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
name varchar(50) NOT NULL,
UNIQUE KEY uk_sessions(name))
COLLATE utf8_unicode_ci;

CREATE TABLE blocks(
block_id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
name varchar(50) NOT NULL,
UNIQUE KEY uk_blocks(name))
COLLATE utf8_unicode_ci;

CREATE TABLE edot(
edah_id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
name varchar(50) NOT NULL,
UNIQUE KEY uk_edot(name))
COLLATE utf8_unicode_ci;

CREATE TABLE campers(
camper_id int NOT NULL AUTO_INCREMENT PRIMARY KEY,
edah_id int,
FOREIGN KEY fk_edah_id(edah_id) REFERENCES edot(edah_id)
ON DELETE SET NULL
ON UPDATE CASCADE,
session_id int,
FOREIGN KEY fk_session_id(session_id) REFERENCES sessions(session_id)
ON DELETE SET NULL
ON UPDATE CASCADE,
first varchar(50) NOT NULL,
last varchar(50) NOT NULL,
email varchar(50) NOT NULL,
needs_first_choice bool DEFAULT 0,
active bool NOT NULL DEFAULT 1)
COLLATE utf8_unicode_ci;

以上一切正常。当我尝试这样做时出现问题：

CREATE TABLE block_instances(
block_id int NOT NULL,
FOREIGN KEY fk_block_id(block_id) REFERENCES blocks(block_id)
ON DELETE CASCADE
ON UPDATE CASCADE,
session_id int,
FOREIGN KEY fk_session_id(session_id) REFERENCES sessions(session_id)
ON DELETE SET NULL
ON UPDATE CASCADE,
PRIMARY KEY pk_block_instances(block_id, session_id))
COLLATE utf8_unicode_ci;

这个returns

ERROR 1005 (HY000): Can't create table 'chugbot_db.block_instances' (errno: 150)

如果我将第二个 ON DELETE SET NULL 更改为 ON DELETE CASCADE，错误就会消失：

CREATE TABLE block_instances(
block_id int NOT NULL,
FOREIGN KEY fk_block_id(block_id) REFERENCES blocks(block_id)
ON DELETE CASCADE
ON UPDATE CASCADE,
session_id int,
FOREIGN KEY fk_session_id(session_id) REFERENCES sessions(session_id)
ON DELETE **CASCADE**
ON UPDATE CASCADE,
PRIMARY KEY pk_block_instances(block_id, session_id))
COLLATE utf8_unicode_ci;

工作正常。

谁能告诉我在 block_instances table 中使用 ON DELETE SET NULL 有什么问题吗？好像和campers里面的ON DELETE SET NULL一模一样table.

Answer 1

这原来是 MySQL 中的错误：

http://bugs.mysql.com/bug.php?id=80052

MySQL 拒绝带有 ON DELETE SET NULL 但不是 ON DELETE CASCADE 的列

MySQL rejects column with ON DELETE SET NULL but not ON DELETE CASCADE

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